The invention is a method and a device that allows for the electrical emulation of the microsurgical abilities of pulsed lasers. These lasers are the basis for new laser procedures that are responsible for high speed and high precision cutting action in biological liquid environments with minimal damage to the surrounding mechanism. They work by producing cavitation bubbles. The action of these lasers and laser procedures are simulated in the current invention by using protocols that are a part of this invention. These protocols regulate the electrical current injected into the specialized device that has been devised. As a result it is possible to emulate the cavitation bubble formation cutting that has become a hallmark of various pulsed laser procedures. The invention allows the same device to be used for such an emulation of these cavitation bubbles while also allowing for heat induced coagulation and poration of biological materials.
Various pulsed lasers have been applied to soft tissue cutting and removal in a liquid environment. Three basically different mechanisms of light absorption have been involved in laser surgery: (1) linear absorption of light by tissue (I. Turovets, D. Palanker, Y. Kokotov, I. Hemo, A. Lewis, J. Appl. Phys. 79(5):2689-2693 (1996); D. Palanker, I. Turovets, A. Lewis, Laser-Tissue Interaction VII, Proc. SPIE 2681 (1996)); (2) linear absorption of light by the medium (P. D. Brazitikos, D. J. D""Amico, M. T. Bernal, A. W. Walsh, Ophthalmology 102(2):278-290 (1994) ; C. P. Lin, D. Stern, C. A. Puliafito, Invest. Ophthalmol. Vis. Sci 31(12):2546-2550 (1990)); or (3) non-linear absorption by tissue or medium associated with dielectric breakdown of the material (A. Vogel, S. Busch, K. Jungnickel, R. Birngruber, Lasers Surg. Med. 15:32-43 (1994)). In spite of differences in the mechanisms of laser radiation absorption in tissue, the mechanism of tissue disruption with pulsed lasers has been generally associated with an explosive expansion of overheated liquid and subsequent cavitation bubble formation. As a result, material disruption occurs in the light absorption zone and in a zone of fast expansion and collapse of cavitation bubbles (I. Turovets, D. Palanker, Y. Kokotov, I. Hemo, A. Lewis, J. Appln. Phys. 79(5): 2689-2693 (1996); P. D. Brazitijos, D. J. D""Amico, M. T. Bernal, A. W. Walsh, Ophthalmology 102(2): 278-290 (1994); and A. Vogel, S. Busch, K. Jungnickel, R. Birngruber, Lasers Surg. Med. 15: 32-43 (1994)).
In view of the general complicated nature of laser-based devices a search was made for ways to emulate with non-laser methodologies the mechanisms that are known to occur with available lasers. In the case of cavitation bubble generation it is known, as described above, that these bubbles result from local and fast heat energy deposition. Thus, it is logical to consider an overheating of a conductive medium with a short pulse of electric current in order to generate an action which is similar to such pulsed laser. The invention described herein realizes such electro microsurgery in a physiological medium with a specific potential for applications in ophthalmology. Previous investigators who have considered pulsed electrical techniques and have seen cavitation bubble formation (R. Vorreuther, R. Corleis, T. Klotz, P. Bernards, U. Englemann, J. Urology 153:849-853 (1995); R. Lemery, T. K. Leung, E. Lavallee, A. Girard, M. Talajic, D. Roy, M. Montpetit, Circulation 83 (1):279-293 (1991)) considered these bubbles either as an undesired side effect or as a means for shock wave generation for hard tissue destruction. These electrosurgical devices were designed for relatively high energy pulse generation: between 25 mJ and 40 J and with relatively long pulse duration: hundreds of microseconds. Such high energy pulses resulting in a few millimeter-sized cavitation bubbles cannot be applied to microsurgical applications such as those envisioned in delicate organs such as the eye. To accomplish such delicate cavitation bubble based microsurgery, a new electrical system based on an asymmetric microelectrode that enables generation of hundreds of thousands of cavitation bubbles, is described. This can become an alternative to endo-laser equipment in such areas as vitreoretinal surgery.
The concept can also be extended to the electroporation of individual cells and assemblies of cells in which the state of the prior art is a macroscopic device with macroscopic electrodes placed in a large bath with a solution of cells (M. Joersbo and J. Brunstedt, Physiologia Plantarium 81:256-264 (1991)). Instead of this a microelectrode for local electroporation of individual cells is used, or alternatively, an array of microelectrodes could be applied for poration of assemblies of cells.
In addition, by varying the nature of the characteristics of the electrical current the same device can be used for cavitation bubble cutting, electroporation or coagulation.
Electrosurgical devices are widely used in surgery. The majority of these techniques are based on heating the tissue by an RF current and this local heat deposition causes one of the following processes: coagulation, and/or water evaporation. As a result, the only capability of such devices is to cut soft tissues by heat deposition which causes significant coagulation in the area surrounding the cut tissue. Such devices are totally useless for endolaser applications, for example in the eye. In addition to such RF techniques, DC pulsed electrical methodologies have not achieved a widespread acceptance because the absence of coagulation was considered an undesirable effect. In the past, cavitation bubbles were generated by DC pulsed methodologies. However, these techniques, which were designed for relatively high energy pulse generation (tens of milliJoules) with relatively long pulse durations (hundreds of microseconds), were only used as a means for shock wave generation for hard tissue destruction (R. Vorreuther, R. Corleis, T. Klotz, P. Bernards, U. Engelmann, J. Urology 153:849-853 (1995)). These high energy pulses resulted in cavitation bubbles with dimensions of a few millimeters, and these have no applicability to, for example, eye microsurgery in which considerably smaller bubbles are required. Laser-based techniques indicate that the pulse energies required to produce such bubbles are in the range of a few tens of microjoules and the pulse durations required are generally in a sub-microsecond range (D. Palanker, I. Hemo, I. Turovets, H. Zauberman, A. Lewis, Invest Ophthal. Vis. Sci. 35:3835-3840 (1994); C. P. Lin, Y. K. Weaver, R. Birngruber, J. P. Fujimoto, C. A. Puliafito, Lasers Surg. Med. 15:44-53 (1994)). In addition to these differences in the time/energy characteristics of the available DC pulsed technologies as compared the present invention, it is required that any device for applications such as vitreoretinal surgery should be able to withstand tens of thousands of pulses. The previous high energy devices described above have a lifetime of less than 100 pulses (R. Vorreuther, R. Corleis, T. Klotz, P. Bernards, U. Engleman, J. Urology 153:849-853 (1995) and this is by far not sufficient for the microsurgical applications that are envisioned.
In terms of cell poration, the prior art were again macroscopic devices with macroscopic electrodes placed in a large bath (M. Joersbo and J. Brunstedt, Physiologia Plantarium 81:256-264 (1991)) with a solution of cells.
The method and device of the present invention are based on producing sub-microsecond high voltage discharges in physiological media with special protocols designed for the generation of cavitation bubbles for soft tissue microsurgery in a liquid environment as is possible today with certain pulsed lasers. The device consists of a combination of three elements:
a specific microelectrode structure,
specific electrical protocols to develop the required pulse characteristics to emulate pulsed laser microsurgery with cavitation bubble generation in the same device that can produce other electrical protocols for tissue coagulation and electroporation; and
the above protocols determine the characteristics of the HV pulse generator that is to be used.